The engine in the 318i is not the 3 cylinder. Both engines are 2.0 litre in size and both have four cylinders, the 318i produces 156hp and 0-62mph is achievable in 8.4 seconds producing 250nm of torque. The 320i has 184hp and 0-62 is a sprightly 7.1 seconds. Both engines claim economy to be 41.5 miles per gallon.